NASA Space Laser Will Follow Earth's Melting Poles and Endangered Ice | Science

Nowhere are the realities of man-made climate change more apparent than on the thaw poles of the Earth. The Arctic pack ice is disappearing as melting ice in Greenland and Antarctica is causing sea level rise to accelerate. Yet for almost a decade, NASA has no dedicated satellite to measure the height of the polar ice – and how it drops as the ice melts or slides into the oceans.

This gap is expected to end with the launch, on September 15, of the $ 1 billion Ice, Cloud and Land Elevation (ICESat-2) satellite at the Air Force Base. Vandenberg, California. ICESat-2 will bounce the laser light off the surface of the Earth, evaluating changes in its elevation as small as the diameter of a pencil. Although the mission is a successor to ICESat-1, which ended in 2010, its multi-beam laser instrument ranks it in a different class, says Ted Scambos, a glaciologist at the National Snow & Ice Data Center in Boulder, Colorado. "Every season we will get a better map than ICESat-1."

While ICESat-1 used a single laser beam, ICESat-2 has three pairs of parallel beams, allowing it to scan multiple paths at once. (Pairings are required to calculate slopes on a given runway, which will help to avoid misinterpretation of ice loss when a slightly shifted back passage identifies changes in altitude. ) Its resolution is also much higher: ICESat-1 ICESat-2 will record every 70 centimeters of altitude, pulling its lasers 10,000 times per second. Frequent shooting means that each pulse is relatively weak; To capture weak reflections, the satellite uses a small telescope to channel the light to sensitive vacuum tubes that can detect single photons. "I'm a physicist and I'm always shocked that it works," says Thorsten Markus, the mission project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The progress of ICESat-2 has not been cheap. The crystals used to amplify its lasers cracked when their metal frames expanded unexpectedly. By repairing them and fixing other complications, the launch date of 2016 has been delayed and costs have risen by several hundred million dollars.

During the long wait, scientists monitored the polar ice with the CryoSat-2 from the European Space Agency (ESA), which uses a radar to detect the height. But its readings have a lower resolution because of its wider radar beam. Beata Csatho, a remote sensing glaciologist at the University of Buffalo, New York State State University. "For Antarctica, this gap is huge. We really do not know what happened.

A first task for ICESat-2 will be to evaluate the white mystery that is the East Antarctic ice sheet, the largest in the world. Extreme cold and high altitude are thought to protect it from major ice loss, but scientists want to understand how snowfall, melting ice and changing bedrock contribute to the minute changes in the weather. elevation. The satellite will also be able to scan the cliffs of the Antarctic Peninsula, which, despite its small size, is responsible for a quarter of the ice losses on the continent. "This will certainly be the first place I'm looking for," says Andrew Shepherd, a glaciologist at the University of Leeds in the UK and senior scientific advisor for CryoSat-2. He notes that the CryoSat-2 radar beam is too wide to allow accurate measurements of ice in the rugged peaks of the peninsula.

Scientists will also use ICESat-2 to monitor the ice sheet groundlines, where glaciers flowing into the ocean begin to float on the bedrock and become ice trays. These shelves are vulnerable to the melting of ocean waters from below, causing the withdrawal of inland baselines. Due to the trough topography of the Antarctic bedrock, glaciologists fear that the retreat may accelerate and expose the ice to more and more water in a feedback process that could cause a rapid collapse of the ice.

The grounding lines are revealed on the surface of a glacier by subtle changes in the slope of the ice to the point where the ice begins to rise and fall with the tides. ICESat-1 could detect grounding lines, but only a few and only for part of the year; ICESat-2 will check them every 3 months. "We're going to have a much better idea where warmer water is getting under the ice," says Helen Fricker, a glaciologist at the Scripps Institution of Oceanography in San Diego, California.

If an ice shelf is about to collapse into the sea, scientists will want to put together an observational campaign right away. Csatho is studying how to use ICESat-2 data in an early warning system that would detect sudden meltdown events in near real-time, rather than a year or two later.

When ICESat-2 does not look at the ice caps, it will measure the canopy height of high latitude forests, providing climatologists with an indirect measure of carbon stored in trees. He will also partner with CryoSat-2 to measure the snow covering the land and sea ice. Since the laser light is bouncing off the snow as the radar reflects from the ice, the combination of both satellite measurements could help the investigators to separate the snow from the ice. In Antarctica, where the drifts can reach nearly 2 meters in height, this could accentuate the measurements of the thickness of the ice. According to Shepherd, NASA and ESA are already considering modifying the CryoSat-2 orbit to create more overlap. The European satellite has enough fuel to move, he adds.

But first, ICESat-2 must reach the orbit and show that its eye on the ice is as clear as promised.